U.S. national team coach Jurgen Klinsmann will be counting on a makeshift defense in the two most critical matches of his tenure -- the upcoming World Cup qualifiers against Costa Rica (Friday) and Mexico (March 26).

Klinsmann announced a 23-man roster Monday afternoon shaped profoundly by injuries, especially in the rear. Goalkeeper Tim Howard (back) and the two outside backs who started last month’s loss in Honduras, Timmy Chandler (hamstring) and Fabian Johnson (hip) are out. Chandler was filling in for Steve Cherundolo (knee), who remains sidelined, while defensive midfielder Danny Williams (undisclosed illness) also is unavailable.

Captain Carlos Bocanegra, who was called up but then benched in Honduras, was not named Monday. He has not been playing regularly for his Spanish club, Racing Santander.

That leaves only two outside backs on the roster -- Real Salt Lake’s Tony Beltran and the San Jose Earthquakes’ Justin Morrow. Each has appeared only once for the national team. Geoff Cameron, who has played in the middle for Klinsmann, has experience on the flanks with Stoke City and might find himself in a wide role against Costa Rica and Mexico.

The U.S. (0-1-0) plays host to Costa Rica (0-0-1) on Friday at Dick’s Sporting Goods Park outside Denver and then will head south to meet Mexico (0-0-1) at the Estadio Azteca four days later. Friday’s game is considered a must-win. The top three finishers in the five-team, double round robin known as the Hexagonal will earn berths in the 2014 World Cup. The fourth place team will face an Oceania representative for a fourth spot in Brazil.

Moving up the field, Klinsmann appears to have responded to his team’s lack of width in Honduras with the addition of Brek Shea (Stoke City) and DaMarcus Beasley (Puebla). Michael Bradley (AS Roma) and Jermaine Jones (Schalke 04) are good bets to start centrally.

There were no surprises among the forward corps. All eyes will be on Jozy Altidore (AZ Alkmaar), who extended his record for an American playing abroad with his 25th goal of the season over the weekend. However, he hasn’t scored for the U.S. since November 2011.

The U.S. is gathering in Denver on Monday to begin preparing for Friday’s qualifier. Here is Klinsmann’s team: